KR20020005444A - Compatible optical pickup apparatus adopting sigle light source - Google Patents

Abstract

PURPOSE: A compatible optical pick-up device employing a single optical source is provided, which uses a single optical source that emits beams having wavelengths longer than 650nm so as to employ both of CD and DVD. CONSTITUTION: The compatible optical pick-up device includes a single optical source(50), an objective lens(70), an optical path converter, and a light detector. The single optical source emits beams having wavelengths longer than 650nm. The objective lens focuses a beam emitted from the optical source to form light spots on the first and second optical discs(40a,40b). The first optical disc is relatively thin and the second optical disc is relatively thick. The optical path converter is arranged between the optical source and the objective lens and changes the traveling path of an incident light. The light detector receives light that was reflected from the optical disc and passed the objective lens and optical path converter to detect an information signal and/or error signal.

Description

Compatible optical pickup apparatus adopting sigle light source

The present invention relates to a compatible optical pickup device capable of interchangeably employing CD and DVD optical discs, and more particularly, to a compatible optical pickup device employing a single light source that emits light having a wavelength longer than 650 nm. It is about.

In general, an optical pickup device is a device that performs recording / reproducing of information on a recording medium in a non-contact manner. An optical pickup apparatus capable of recording / reproducing a DVD-based optical disc (hereinafter, DVD) having a thickness of 0.6 mm employs an objective lens having a numerical aperture of 0.6 and a light source that emits light having a wavelength of 650 nm. At this time, the DVD optical pickup device should also be compatible with the existing CD-based optical disk (hereinafter, referred to as CD) having a thickness of 1.2mm.

In view of such a situation, conventionally, optical pickup devices capable of interchangeably employing optical discs having different formats have been proposed.

The conventional optical pickup apparatus employing CD and DVD compatible has a structure employing two light sources (1) (3) for emitting light of different wavelengths, as shown in FIG.

Referring to FIG. 1, the first light source 1 emits light having a wavelength of 635 or 650 nm and is used to record / reproduce the DVD 10a having a relatively thin thickness. The second light sources 3 and 3 emit light of 780 nm wavelength and are used to record / reproduce the CD 10b having a relatively thick thickness.

The light emitted from the first light source 1 side passes through the first beam splitter 7 and is then reflected by the second beam splitter 9 to be directed toward the optical disc 10. The light emitted from the second light source 3 is sequentially reflected by the first and second beam splitters 7 and 9 and directed toward the optical disc 10. The objective lens 15 focuses the light incident from the first and second light sources 1 and 3 to form an optical spot on the optical disc 10. At this time, the light emitted from the first light source 1 is formed in the DVD 10a having a relatively thin thickness, and the light emitted from the second light source 3 is formed in the CD 10b having a relatively thick thickness.

On the other hand, the light reflected from the disk 10 is incident on the second beam splitter 9 via the objective lens 15, and passes through most of the second beam splitter 9 and is received by the photodetector 19. .

Here, reference numeral 5 denotes a grating which diffracts the light incident from the second light source 3 side into the 0th order and ± 1st order light so as to detect the tracking error signal by the 3-beam method when recording / reproducing the CD 10b. Reference numeral 11 denotes a collimating lens for converting divergent light incident from the first and second light sources 1 and 3 into parallel light, and reference numeral 17 is reflected from the disk 10 and the second beam splitter 9 The photodetecting lens 17 is configured to focus the incident light through the light and to be received by the photodetector 19.

The conventional compatible optical pickup apparatus as described above includes two light sources 1 and 3 for emitting light of different wavelengths, so that both CD-based optical discs and DVD-based optical discs can be employed.

However, the conventional compatible optical pick-up apparatus as described above has two problems, since the two light sources 1 and 3 have high manufacturing cost, their structure is complicated, and assembly and optical arrangement are difficult.

Moreover, the 635 or 650 nm wavelength light source 1 capable of outputting recording power for DVD-R, DVD-RAM and the like has a very high cost, which is a major obstacle to achieving low cost of a compatible optical pickup device.

The present invention has been made in view of the above-mentioned point, and adopts a single light source that emits light having a wavelength longer than 650 nm, thereby making it possible to use a CD-based and DVD-based optical discs in a compatible manner. The purpose is to provide a device.

1 is a view schematically showing an example of a conventional compatible optical pickup device;

2 is a view schematically showing an optical configuration of a compatible optical pickup device employing a single light source according to an embodiment of the present invention;

3 is a graph schematically showing reflectances before and after recording according to wavelengths of cyanine-based CD-Rs and Phthalo-based CD-Rs which are currently commercially available;

4 is a graph schematically showing reflectances before and after recording according to wavelengths of Azo-based DVD-Rs and cyanine-based DVD-Rs which are currently commercially available;

5 is a plan view showing an objective lens according to the present invention employed in FIG.

6 and 7 schematically show an embodiment of an objective lens according to the present invention employed in FIG. 2, respectively.

8 is a view schematically showing an optical configuration of a compatible optical pickup apparatus employing a single light source according to another embodiment of the present invention;

9 is a schematic view showing an optical configuration of a compatible optical pickup apparatus employing a single light source according to another embodiment of the present invention;

10A and 10B are aberration diagrams showing aberration characteristics according to the incident beam field of the objective lens and the conventional 650nm objective lens according to the present invention;

11A and 11B are aberration diagrams showing aberration characteristics according to the inclination of the optical disk of the objective lens according to the present invention and the conventional 650nm objective lens,

12 is a graph showing a reproduction signal value according to the pit depth when a DVD is reproduced by the compatible optical pickup apparatus according to the present invention.

<Description of the symbols for the main parts of the drawings>

40 Optical disc 40a, 40b First and second optical disc 50 Light source

60 Hologram splitter 61 Polarization hologram element 63163 Wavelength plate

70 objective lens 71,75 paraxial and circular region 73 annular lens region

A compatible optical pickup device according to the present invention for achieving the above object, and a single light source for emitting light of a wavelength longer than 650 nm; Paraxial region, ring-shaped annular lens region, and circular axis around the vertices to focus light incident on the light source to form a light spot suitable for a relatively thin first optical disk and a relatively thick second optical disk, respectively. An objective lens for forming a light spot having a half width (FWHM) of 0.72 μm or less for the first optical disk and a light spot having a half width of 0.8 μm or more for the second optical disk; An optical path converter disposed on an optical path between the light source and the objective lens to convert an advancing path of incident light; And a light detector that is reflected from the optical disk and receives the light incident through the objective lens and the optical path converter to detect an information signal and / or an error signal.

Here, it is preferable that the first optical disc is a DVD-based optical disc, and the second optical disc is a CD-based optical disc.

The light source preferably emits light having a wavelength of about 680 nm to 780 nm.

Preferably, the objective lens has a numerical aperture of 0.63 or more for the first optical disk, and a numerical aperture of 0.53 or less for the second optical disk.

In the objective lens, when the first optical disk is employed, light passing through the paraxial region and the circular axis region is focused as an optical spot on the information recording surface of the first optical disk, and when the second optical disk is employed, the optical lens passes through the paraxial region and the annular lens region. Preferably, the annular lens area is optimized for the second optical disc so that light is focused on the information recording surface of the second optical disc as an optical spot.

On the other hand, the light source is a corner light emitting laser or a surface light laser, the optical path converter comprises: a polarizing hologram element for diffracting incident light in 0th order, + 1st order and / or -1st order according to the linear polarization component; It may include a; wave plate for changing the polarization of the incident light.

Here, the optical path converter may include a beam splitter disposed between the light source and the objective lens to transmit or reflect incident light. When the beam splitter is configured to transmit or reflect incident light according to polarized light, the beam splitter may be disposed between the beam splitter and the objective lens to convert polarized light of the incident light.

A compatible optical pickup device according to the present invention for achieving the above object, and a single light source for emitting light of a wavelength longer than 650 nm; Paraxial region, ring-shaped annular lens region, and circular axis around the vertices so as to focus light incident on the light source to form suitable light spots on the first relatively thin optical disk and the second relatively thick optical disk, respectively. An objective lens having a region, the objective lens having an effective numerical aperture of 0.63 or more for the first optical disk, and an effective numerical aperture of 0.53 or less for the second optical disk; An optical path converter disposed on an optical path between the light source and the objective lens to convert an advancing path of incident light; And a light detector that is reflected from the optical disk and receives the light incident through the objective lens and the optical path converter to detect an information signal and / or an error signal.

Hereinafter, preferred embodiments of the compatible optical pickup apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a view schematically showing an optical configuration of a compatible optical pickup apparatus according to an embodiment of the present invention.

Referring to the drawings, a compatible optical pickup device according to an embodiment of the present invention, a single light source 50 to emit light of a wavelength longer than 650 nm, and an actuator (not shown) for focusing and tracking control An objective lens 70 mounted and driven to focus light incident from the light source 50 to form light spots suitable for the first and second optical discs 40a and 40b having different thicknesses, respectively, and the light source 50 And an optical path converter disposed on the optical path between the objective lens 70 and the objective lens 70 to convert the advancing path of the incident light, and the photodetector 100 to receive the light reflected from the optical disc 40. Here, the first optical disk 40a is a relatively thin DVD-based optical disk, and the second optical disk 40b is a relatively thick CD-based optical disk.

The light source 50 includes a semiconductor laser that emits high output light to be used for recording as well as information signal reproduction, that is, an edge emitting laser or a vertical cavity surface emitting laser. It is preferable.

The light source 50 emits light having a wavelength longer than 650 nm, for example, a wavelength between approximately 660 nm and 790 nm. Here, it is more preferable that the light source 50 emits light having a wavelength between 680 nm and 780 nm.

Here, with respect to the recording power for DVD-R, DVD-RAM and the like, the semiconductor laser for wavelength longer than 650 nm is much lower in cost than the semiconductor laser for 650 nm wavelength.

Therefore, according to the present invention, the unit cost of the light source 50 can be significantly lowered than in the related art. For example, when the 680 nm semiconductor laser is employed as the light source 50, the 680 nm semiconductor laser has a very low unit cost compared to the 650 nm semiconductor laser employed as a conventional DVD light source. The manufacturing cost of the compatible optical pickup apparatus according to the present invention can be greatly reduced.

On the other hand, since the CD-R has an organic dye film recording layer having a large absorption rate for light having a wavelength of 750 nm or less, in order to employ CD-R, wavelengths of 750 nm or more are used to prevent destruction of recording data due to sensitivity difference. It is necessary to employ a light source that emits light.

On the other hand, when employing a semiconductor laser that emits light of a wavelength smaller than 770 nm, more preferably 760 ± 10 nm as the light source 50, the compatible optical pickup device according to the present invention is low cost At the same time, there is an advantage in that the commercially available CD-R and DVD-R can be used interchangeably regardless of the type of organic dye used. Here, CD-R and DVD-R which are currently commercialized have different absorption rate characteristics depending on the type of organic dye film used. That is, currently commercialized cyanine-based CD-R and Phthalo-based CD-R are optimized to have a large reflectance difference before and after recording for 780 nm wavelength, as shown in FIG. The difference in reflectance before and after recording by wavelength has different characteristics depending on the organic dye used. In particular, CD-R has a large absorption rate for light having a wavelength of 750 nm or less. Therefore, in order to employ even the CD-R, it is necessary to employ a light source that emits light having a wavelength of 750 nm or more in order to prevent destruction of recording data due to sensitivity difference. In addition, Azo-based DVD-R and cyanine-based DVD-R, which are currently commercialized, are optimized to have a large difference in reflectance before and after recording for 650 nm wavelength, as shown in FIG. 4. Similarly, the difference in reflectance before and after recording by wavelength has different characteristics depending on the organic dye used. In particular, in the azo DVD-R, the reflectance is reversed in the wavelength region longer than approximately 770 nm (the reflectance before recording becomes smaller than that after recording), or the difference in reflectance before and after recording approaches zero. Therefore, in consideration of reflectance characteristics before and after recording of DVD-R and CD-R according to the organic pigment type and absorption of CD-R, as shown in FIGS. 3 and 4, the light source 50 is larger than 750 nm. By employing a light source having a long wavelength shorter than 770 nm, for example, a 760 nm wavelength, CD-R and DVD-R can also be compatible regardless of the type of organic dye used.

Here, if the CD-R is manufactured to have a small absorption rate even for light having a wavelength of 750 nm or less, the compatible optical pickup apparatus according to the present invention can adopt the CD-R compatible regardless of the wavelength region of the light source 50 employed. It becomes possible. In addition, if, for example, the azo-based DVD-R is manufactured such that the reflectance is not reversed even for light having a wavelength of 770 nm or more, or the reflectance difference before and after recording is large, the compatible optical pickup apparatus according to the present invention is a wavelength region of the light source employed. Regardless of whether or not the DVD-R can be used.

On the other hand, as described above, when a semiconductor laser is provided as the light source 50, light linearly polarized in one direction is emitted from the light source 50.

Therefore, a hologram comprising a polarization hologram element 61 which diffracts incident light in the 0th order, + 1st order and / or -1st order according to the linear polarization component and the wave plate 63 for changing the polarization of the incident light with the optical path converter. It is preferable to provide the fluorescent splitter 60. In this case, the light emitted from the light source 50 is mostly irradiated to the optical disk 40, and the light emitted from the optical disk 40 is mostly received by the photodetector 100, so that the light utilization efficiency is high.

The polarization hologram element 61 is preferably arranged to diffract light linearly polarized in one direction incident from the light source 50 toward the 0th order. In addition, the wave plate 63 is preferably provided with a quarter wave plate 63 with respect to the wavelength of the light emitted from the light source 50, and is incident from the light source 50 side. It is preferable to arrange | position so that linearly polarized light may be changed to circularly polarized light.

Accordingly, light linearly polarized in one direction incident from the light source 50 is diffracted in the 0th order in the polarization hologram element 61, and is converted into one circularly polarized light via the wave plate 63 and is made by the optical lens by the objective lens 70. Is focused on the information recording surface (40). The focused light is reflected by the information recording surface of the optical disk 40 and is converted into other circularly polarized light, and is linearly polarized light in the other direction via the wave plate 63 again, and is polarized by the polarization hologram element 61. Diffracted first-order and / or first-order to the photodetector 100.

The photodetector 100 receives the light reflected from the optical disk 40 and incident through the objective lens 70 and the holographic light splitter 60 to detect an information signal and / or an error signal. The photodetector 100 is provided with a plurality of dividers (not shown) for photoelectric conversion each independently so as to detect focus and tracking error signals.

As shown in FIG. 2, the optical detector 100 may be installed on the same base 101 as the light source 50, as shown in FIG. 2. It can be modular with the light source 50.

In this case, the hologram-type splitter 60 is a light that is incident on the light source 50 side is mostly diffracted in order of zero, and the light incident on the optical disc 40 is mostly diffracted in +1 order and / or -1 order. An element (not shown) may be provided.

Here, reference numeral 65 is a collimating lens that converts the divergent light incident from the light source 50 into parallel light to form an infinite optical system. The collimating lens 75 is preferably disposed between the optical path converter and the objective lens 70. In this case, the collimating lens 75 converts the divergent light incident from the light source 50 into parallel light and simultaneously converts the incident light reflected from the optical disk 40 into focused light so as to face the photodetector 100. .

As shown in FIG. 5, the objective lens 70 includes a paraxial region 71, a ring-shaped annular lens region 73, and a circular axis region 75. Here, the vertex is a point where the central axis of the objective lens 70 and the surface of the objective lens 70 meet.

The annular lens area 73 is an area in which light in an intermediate region between the paraxial region 71 and the circular axis region 75 of incident light is incident, and faces or faces the light source 50 of the objective lens 70. It is formed in the shape of an oval ring or a circular ring on the side facing the medium 40.

According to a preferred embodiment of the present invention, it is preferable that the annular lens region 73 is formed in an aspherical shape as shown in FIG. 6, and is optimized for a relatively thick second optical disk 40b.

As described above, if the annular lens area 73 is an aspherical shape optimized for the second optical disk 40b, the paraxial region 71 of the light emitted from the light source 50 when the relatively thin first optical disk 40a is employed. ) And the light passing through the circular axis region 75 are collected as an optical spot on the information recording surface of the first optical disk 40a, and the circular lens region 73 which is an intermediate region between the paraxial region 71 and the circular axis region 75. The light passing through) is scattered to such an extent that information cannot be read from the information recording surface of the first optical disk 40a.

When the second optical disk 40b having a relatively thick thickness is employed, the light passing through the paraxial region 71 and the annular lens region 73 of the light emitted from the light source 50 is transferred to the second optical disk 40b. The light is condensed on the information recording surface of the light spot, and the light passing through the circular axis area 75 is scattered to such an extent that information cannot be read from the information recording surface of the second optical disk 40b.

Alternatively, the annular lens region 73 may be formed to block or scatter incident light, as shown in FIG. 7. In this case, when the first optical disk 40a having a relatively thin thickness is employed, the light passing through the paraxial region 71 and the circular axis region 75 of the light emitted from the light source 50 is transferred to the first optical disk 40a. Light condensed on the information recording surface as a light spot, and the light passing through the annular lens area 73 is blocked or scattered and cannot be condensed on the information recording surface of the first optical disk 40a. In addition, when the second optical disk 40b having a relatively thick thickness is employed, the light passing through the paraxial region 71 of the light emitted from the light source 50 is a light spot on the information recording surface of the second optical disk 40b. Condensed On the other hand, the light passing through the circular axis area 75 is not focused on the information recording surface of the second optical disc 40b with an intensity suitable for recording and / or reproduction, and the light passing through the annular lens area 73 is As a result, it is blocked or scattered so that it cannot be focused on the information recording surface of the second optical disk 40b.

The objective lens 70 according to the present invention having the above structure condenses the light incident from the light source 50 and is suitable for the first and second optical disks 40a and 40b having different thicknesses, respectively. It is provided to form. That is, the objective lens 70 according to the present invention forms an optical spot having a half width (FWHM) of 0.72 μm or less (1.2 μm or less in 1 / e ² ) with respect to the first optical disk 40a, and the second For the optical disc 40b, it is preferable to form an optical spot having a half width of 0.8 μm or more (the width at 1 / e ² is 1.3 μm or more).

In order to form a light spot of the size as described above, the objective lens 70 according to the present invention has a numerical aperture correlated with the wavelength of the light emitted from the light source 50. That is, when the light source 50 emits light having a wavelength between 680 nm and 780 nm, the objective lens 70 according to the present invention has an effective numerical aperture of 0.63 or more for the first optical disk 40a, and the second optical disk 40b. ), It is preferable to have an effective numerical aperture of 0.53 or less.

As a more specific example, when the light source 50 emits light having a wavelength of 680 nm, 720 nm, 760 nm or 780 nm, the objective lens 70 is approximately 0.63, 0.66, 0.7 with respect to the first optical disk 40a. Or an effective numerical aperture of 0.72. In addition, when the light source 50 emits light having a wavelength of approximately 750 to 770 nm, it is preferable that the objective lens 70 has an effective numerical aperture of 0.7 or more for DVD and 0.53 or less for CD. Do. For example, when the light source 50 emits light having a wavelength of 760 ± 10 nm, it is preferable that the objective lens 70 has an effective numerical aperture of 0.7 for DVD and 0.53 for CD.

Here, FIG. 2 illustrates a case in which the objective lens 70 including the annular lens region 73 having an aspherical shape described with reference to FIG. 6 is employed. In particular, in order to show the focusing of light according to the incident region, FIG. Lens 70 is shown conceptually.

2, 6, and 7, the light incident surface of the second optical disk 40b, which is relatively thick, is closer to the objective lens 70 than the light incident surface of the first optical disk 40a, which is relatively thin. It is shown as being located, which is intended to show the difference in distance between the light incident surface of the first and second optical disks 40a and 40b and the objective lens 70, that is, the difference in working distance. In the actual system, the light incidence surfaces of the first and second optical disks 40a and 40b are at the same position, and when the second optical disk 40b is employed, the objective lens 70 is driven by an actuator so that the first optical disk 40a can be used. It is moved to adjust the working distance toward the second optical disk 40b than at the time of adoption.

Meanwhile, the compatible optical pickup apparatus according to the present invention may include a beam splitter type optical path converter as shown in FIGS. 8 and 9. That is, as shown in FIG. 8 as an optical path converter, a polarization beam splitter 161 disposed between the light source 50 and the objective lens 70 to transmit or reflect incident light according to polarization, and the polarization beam splitter 161. ) And a wavelength plate 163 disposed between the objective lens 70 and the polarization of incident light. In addition, as shown in FIG. 9, a light splitter 260 may include a beam splitter 260 that transmits and reflects incident light at a predetermined ratio between the light source 50 and the objective lens.

When the beam splitter-type optical path converter is provided as described above, a light receiving lens 167 is further provided on the optical path between the optical path converter and the photodetector 100 to focus incident light to be received by the photodetector 100.

In addition, the compatible optical pickup apparatus according to the present invention may further include a diffraction element 250 for diffracting the light emitted from the light source between the light source 50 and the optical path converter, for example as shown in FIG. Can be. The diffraction element 250 is used to detect a tracking DPP (Differential Push-Pull) signal when a DVD-RAM is played back, or to detect a three-beam tracking signal when a CD is played. The diffraction element 250 may be provided for DVD-RAM and CD playback, respectively. The diffraction element 250 may be similarly applied to the compatible optical pickup apparatus shown in FIGS. 2 and 8.

In FIGS. 8 and 9, the remaining members are the same as those described with reference to FIG. 2, and therefore, the same members will be denoted by the same reference numerals and description thereof will be omitted.

Compatible optical pickup device according to the present invention is not limited to the optical configuration shown in Figures 2, 8 and 9, of course, various modifications are possible.

The compatible optical pickup apparatus according to the embodiments of the present invention as described above employs a single light source 50 that emits light having a wavelength longer than 650 nm, preferably a wavelength between 680 nm and 780 nm. Anger can be achieved. In addition, the compatible optical pickup apparatus according to the present invention has an objective lens designed to have an effective numerical aperture suitable for the first and second optical disks 40a and 40b, respectively, in association with the wavelength of the light emitted from the single light source 50. 70, an optical spot having a half width of 0.72 m or less can be formed on the first optical disk 40a, and an optical spot having a half width of 0.8 m or more can be formed on the second optical disk 40b. Accordingly, the compatible optical pickup apparatus according to the present invention may employ the first and second optical disks 40a and 40b having different thicknesses. Of course, when the light source having a wavelength of 750 nm or more is used as the light source 50, recording / reproducing of the commercially available CD-R is also possible. In addition, by employing a light source having a wavelength of 750 nm or more and 770 nm or less as the light source 50, recording / reproducing of commercially available CD-R and DVD-R is also possible.

Hereinafter, referring to Tables 1, 10A and 10B, 11A and 11B, the objective lens according to the present invention designed to be compatible with the first and second optical disks 40a and 40b for the 780 nm wavelength. The characteristics of the conventional DVD objective lens (not shown: 650 nm objective lens) for 70 and the 650 nm wavelength are compared with each other.

In Table 1, the data values for the objective lens 70 of the present invention are examples of design values for the first optical disk 40a, that is, DVD. In addition, the working distance represents the distance between the surface facing the optical disk 40 of the objective lens 70 and the light incident surface of the optical disk 40, and the working distance of the second optical disk 40b, that is, the CD is reduced by 0.3 mm. . On the other hand, the aberration characteristics of Figs. 10A to 11B are for DVD. Values of 0.04 lambda, shown in dashed lines in FIGS. 10A-11B, indicate the optical aberrations (OPDrms) allowable for a DVD in an optical disc 40 system.

Objective lens (present invention) Objective lens (conventional) Remarks NA 0.73 0.61 Working distance (mm) 1.3 1.8 0.3 mm shrinkage when using CD Effective diameter (mm) 4.09 4.03 Focal Length (mm) 2.8 3.3 Maximum angle of lens curve 55 ° 51 ° Can be made OPDrms at field height 1.0。 0.033λ 0.060λ OPDrms when optical disc tilt is 0.35。 0.041λ 0.038λ Optical disc tolerance tilt 0.35 °

Referring to Table 1, the objective lens for 650 nm has a numerical aperture of 0.61 while the objective lens 70 of the present invention can be designed to have a numerical aperture of 0.73. That is, the 780 nm objective lens 70 of the present invention has a larger numerical aperture than the conventional 650 nm objective lens. The objective lens for 650 nm has an operating distance of 1.8 mm, while the objective lens 70 of the present invention has an operating distance of 1.3 mm. Of course, when the CD is employed, its working distance is further reduced by 0.3 mm, as can be seen in FIGS. 2 and 6 to 9. The objective lens for 650 nm has an effective diameter of 4.03 mm and a focal length of 3.3 mm, whereas the objective lens 70 of the present invention has an effective diameter of 4.09 mm and a focal length of 2.8 mm. The objective lens for the 650 nm has a maximum angle of 51 ° while the objective lens 70 of the present invention is manufactured such that the maximum angle of the lens curve is 55 °. This maximum angle is a manufacturable value.

Referring to FIGS. 10A and 10B showing aberration characteristics according to the incident beam field of the objective lens 70 and the 650 nm objective lens designed according to the data of Table 1, for a field height of 1.0 ° The objective lens 70 of the present invention exhibits an OPDrms of 0.06 lambda, while the objective lens 70 of the present invention exhibits an OPDrms of 0.033 lambda. Here, field aberration occurs when light emitted from a light source enters an objective lens with an inclination angle. Therefore, it is preferable that the objective lens has a field aberration of 0.04 lambda rms or less, which is an optical aberration tolerance value even with respect to the 1 degree field height in consideration of the assembly tolerance of the optical pickup apparatus.

11A and 11B showing the aberration characteristics of the objective lens 70 of the present invention designed with the data of Table 1 and the tilt of the optical disk 40 of the objective lens for 650 nm, the allowable tilt value of the optical disk system is 0.35 °. For the optical disk 40 tilt, the objective lens 70 of the present invention exhibits an OPDrms of 0.041 lambda, which is similar to the OPDrms of 0.038 lambda of the objective lens 70 for 650 nm.

As can be seen from above, the objective lens 70 of the present invention designed for 780 nm when adopting DVD exhibits aberration characteristics similar to or better than that of the conventional DVD objective lens designed for 650 nm. In addition, the objective lens 70 of the present invention has a numerical aperture larger than that of the conventional DVD objective lens, so that even if light having a wavelength larger than 650 nm is used, a small spot suitable for recording / reproducing DVD can be formed. Can be. Therefore, the compatible optical pickup apparatus employing a single light source for wavelength longer than 650 nm according to the present invention can employ not only the CD-based second optical disk 40b but also the DVD-based optical disk 40. FIG.

Here, the size of the light spot is proportional to λ / NA (λ: wavelength, NA: numerical aperture of the objective lens 70). Therefore, since the objective lens 70 of the present invention has a numerical aperture larger than that of the ordinary DVD objective lens, the DVD-type first optical disc 40a can be recorded / reproduced even when light having a wavelength longer than 650 nm is used. It is possible to form small light spots as needed.

Fig. 12 shows the reproduction signal value according to the pit depth when the DVD is reproduced by the compatible optical pickup apparatus according to the present invention. The reproduction signal detected when the DVD having a λ / 6 pit depth is reproduced by the conventional DVD-only apparatus is shown. It is shown for. As can be seen in FIG. 12, for example, when the 780 nm light source 50 and the objective lens 70 having a numerical aperture larger than that of the conventional 650 nm objective lens are adopted for the DVD, the pit depth of the DVD is increased. In the case of lambda / 6, since the reproduction signal can be detected with a magnitude of about 90% of the signal by the conventional DVD-only apparatus, the DVD can be reproduced.

A compatible optical pickup apparatus according to the present invention as described above is designed in association with a single low-cost light source that emits light having a wavelength longer than 650 nm, and the wavelength of the light emitted from this light source, so that a DVD-based optical disc An optical lens with a half-width of 0.72 μm or less is formed, and an optical lens with a half-width of 0.8 μm or more is used for a CD-based optical disc, so that CD- and DVD-based optical discs are compatible with low cost. It can be adopted.

Claims (17)

A single light source emitting light of a wavelength longer than 650 nm; Paraxial region, ring-shaped annular lens region, and circular axis around the vertices so as to focus light incident on the light source to form suitable light spots on the first relatively thin optical disk and the second relatively thick optical disk, respectively. An objective lens for forming a light spot having a half width (FWHM) of 0.72 μm or less for the first optical disk and a light spot having a half width of 0.8 μm or more for the second optical disk; An optical path converter disposed on an optical path between the light source and the objective lens to convert an advancing path of incident light; And an optical detector that is reflected from the optical disk and receives the light incident through the objective lens and the optical path converter to detect an information signal and / or an error signal. The compatible optical pickup apparatus of claim 1, wherein the first optical disk is a DVD-based optical disk, and the second optical disk is a CD-based optical disk. The compatible optical pickup apparatus of claim 1, wherein the light source emits light having a wavelength of approximately 680 nm to 780 nm. 4. The compatible optical pickup apparatus of claim 3, wherein the objective lens has a numerical aperture of 0.63 or more for the first optical disk and a numerical aperture of 0.53 or less for the second optical disk. The compatible optical pickup apparatus of claim 1, wherein the light source emits light having a wavelength of approximately 750 nm to 770 nm. 6. The objective lens of claim 5, wherein the objective lens has an effective numerical aperture of about 0.7 or more for the first optical disk having a relatively thin thickness, and an effective numerical aperture of about 0.53 or less for a second optical disk having a relatively thick thickness. Compatible optical pickup device. The compatible lens according to claim 1, wherein the objective lens has an effective numerical aperture of about 0.7 or more for the first optical disk having a relatively thin thickness, and an effective numerical aperture of about 0.53 or less for the second optical disk. Optical pickup device. The method according to any one of claims 1 to 7, wherein the objective lens, When the first optical disc is employed, the light passing through the paraxial region and the circular axis region is condensed into an optical spot on the information recording surface of the first optical disc, and when the second optical disc is employed, the light passing through the paraxial region and the annular lens region is the second optical disc. And the annular lens area is optimized for the second optical disk so that the information recording surface of the optical disk is focused to an optical spot. The method of claim 1, wherein the light source is a edge-emitting laser or surface light laser, The optical path converter, A polarization hologram element diffracting incident light in 0th order, + 1st order and / or -1st order according to the linear polarization component; And a wave plate for changing the polarization of the incident light. The method of claim 1, wherein the light source is a edge-emitting laser or surface light laser, The optical path converter, And a beam splitter disposed between the light source and the objective lens to transmit or reflect incident light. The method of claim 10, wherein the beam splitter is provided to transmit or reflect incident light according to polarization, And a wavelength plate disposed between the beam splitter and the objective lens to convert the polarized light of the incident light. 12. The compatible optical pickup apparatus of claim 1, 9 or 11, further comprising a collimating lens on an optical path between the optical path converter and the objective lens. A single light source emitting light of a wavelength longer than 650 nm; Paraxial region, ring-shaped annular lens region, and circular axis around the vertices so as to focus light incident on the light source to form suitable light spots on the first relatively thin optical disk and the second relatively thick optical disk, respectively. An objective lens having a region, the objective lens having an effective numerical aperture of 0.63 or more for the first optical disk, and an effective numerical aperture of 0.53 or less for the second optical disk; An optical path converter disposed on an optical path between the light source and the objective lens to convert an advancing path of incident light; And an optical detector that is reflected from the optical disk and receives the light incident through the objective lens and the optical path converter to detect an information signal and / or an error signal. 14. The compatible optical pickup apparatus of claim 13, wherein the first optical disc is a DVD-based optical disc, and the second optical disc is a CD-based optical disc. The compatible optical pickup apparatus of claim 13, wherein the light source emits light having a wavelength of approximately 680 nm to 780 nm. 14. The compatible optical pickup apparatus of claim 13, wherein the light source emits light having a wavelength of approximately 750 nm to 770 nm. The objective lens of claim 13, wherein the objective lens comprises: When the first optical disc is employed, the light passing through the paraxial region and the circular axis region is condensed into an optical spot on the information recording surface of the first optical disc, and when the second optical disc is employed, the light passing through the paraxial region and the annular lens region is the second optical disc. And the annular lens area is optimized for the second optical disk so that the information recording surface of the optical disk is focused to an optical spot.